NetworkServer.dontListen improvements and fixes

[miwarnec]

1. changes double negative 'dontListen=false' to 'listen=true'
2. fixes #2536

MERGE, DONT SQUASH

[miwarnec]

for a simple solution, we could change OnTransprotConnectec to ignore connections while not listening

[MrGadget1024]

for a simple solution, we could change OnTransprotConnectec to ignore connections while not listening

You'd need to call Transport.ClientDisconnect if listen == false so the transport kicks the connection off.

[MrGadget1024]

This in NetworkServer::IsConnectionAllowed

if (dontListen)
{
    Debug.LogError($"Server not listening, client {connectionId} will be kicked");
    return false;
}

[miwarnec]

@MrGadget1024 pushed. no more shutdown. just not accepting connections. that should be the most simple solution here.

[MrGadget1024]

@miwarnec Failing test

[miwarnec]

@miwarnec Failing test

fixed